Offshore drilling is quickly becoming the prevalent method of exploring and producing oil and gas, especially in Western countries where land operations are frequently inhibited by environmental concerns. There is, however, a serious shortfall of offshore drilling units called Mobile Offshore Drilling Units, or MODUs. The relative unavailability of MODUs has resulted in significant delays in many drilling projects. Consequently, the cost of obtaining either a new or existing MODU for an exploration and production operation has dramatically increased over the past decade.
As will be readily appreciated by those of skill in the art, MODUs are utilized during the early testing phase required to evaluate oil, gas, and other hydrocarbon discoveries. However, due to the lack of floating production facilities and the high cost of MODUs, early testing is seldom accomplished, which often results in unnecessary delays and inaccurate predictions of economic assessments, project development schedules, etc. Moreover, procurement of offshore production and storage facilities required to operate offshore projects in a timely manner can be quite difficult. In extreme circumstances or in especially remote regions, the lag time between hydrocarbon discovery and the production phase can reach 10 years or more.
Meanwhile, self-standing riser assemblies supported by buoy devices are becoming a more common method of performing oil and gas exploration and production related activities. Compared to the large scale riser assemblies typically serviced by MODUs, the self-standing riser provides for lighter and less expensive riser tubulars (e.g., drilling pipe, stack casing, etc.). Self-standing risers also admit to the use of lighter blowout preventers, such as those used by land drilling rigs.
Moreover, the top buoy of a self-standing riser system can be positioned near the surface of the water in which it is disposed (for example, less than around 100 ft. below surface level), allowing for efficient drilling in even shallow waters. Furthermore, where riser systems are tensioned and controlled with associated buoyancy chambers, buoy-based systems can be used successfully in much deeper waters.
However, as those of skill in the art have learned in the field, buoy-based systems utilizing general purpose vessels for riser and buoyancy chamber deployment are deficient in that large-scale operations (e.g., deployment in very deep or turbulent waters, or projects involving multiple combinations of riser strings and buoyancy chambers, etc.) are very difficult to control, and thus installation, operation and maintenance of the resulting system is significantly impaired.
There is, therefore, a need for a custom vessel that admits to efficient deployment of large-scale riser systems in a manner similar to the manner of a MODU even when a MODU is not available.